A light-emitting diode lighting device disclosed in Japanese Patent Application Publication No. 2006-147933 (hereinafter referred to as “Document 1”) is an example of the related art. This conventional device is provided with a rectification circuit, a light-emitting diode circuit, a current-limiting resistor element, and a lighting control circuit. The rectification circuit is configured to output a pulsating voltage obtained by full-wave rectification of an AC voltage input from a sine wave AC power supply with an effective value of 100 V. The light-emitting diode circuit is configured by connecting a plurality of light-emitting diodes in series in the same direction. In the light-emitting diode circuit, a plurality of light-emitting diodes is connected in series such that anodes and cathodes thereof are oriented toward a high-potential side and a ground side of the rectification circuit, respectively. Further, the light-emitting diode circuit is divided into a plurality of groups (first diode circuit to sixth diode circuit) by taking a predetermined number of consecutive light-emitting diodes, from among the plurality of light-emitting diodes, as a unit. The current-limiting resistor element is connected between the rectification circuit and light-emitting diode circuit and configured to limit a current flowing through the light-emitting diode circuit.
The lighting control circuit has first to fifth drive switch devices that are separately connected in series with the respective diode circuits. The lighting control circuit is configured to light up the first to sixth light-emitting diodes in a cascade manner by ON/OFF orderly switching the first to fifth drive switch devices according to an instantaneous value of the pulsating voltage output from the rectification circuit.
In the related art example disclosed in Document 1, lighting control of a plurality of light-emitting diodes connected in series can be efficiently performed with a simple circuit configuration by increasing or decreasing the number of lighted light-emitting diodes according to the instantaneous value of a pulsating voltage.
However, in the related art example disclosed in Document 1, since the quantity of light changes according to the increase or decrease in the number of the lighted light-emitting diodes, light blinking sometimes becomes a problem. Frequent changes in screen brightness are particularly undesirable in images captured with video cameras.
Meanwhile, the problems encountered when a smoothing capacitor is connected between output terminals of the rectification circuit and the pulsating voltage is smoothed thereby include the decrease in power factor caused by the increase in the stop period of the input current and an overlarge surge current flowing through the smoothing capacitor when the AC power supply is switched on.